A liquid crystal display device includes a TFT substrate and a color filter substrate. The TFT substrate is configured such that pixel electrodes, thin film transistors (TFTs) and the like are arranged in a matrix form. The color filter substrate is disposed opposite to the TFT substrate in which color filters and the like are formed at locations corresponding to the pixel electrodes of the TFT substrate. A liquid crystal is interposed between the TFT substrate and the color filter substrate. Then, an image is formed by controlling the transmittance of light of the liquid crystal molecules for each pixel.
The liquid crystal display device can be made small and thin, and is used in a wide range of applications such as mobile phones and other electronic devices. In recent years, various types of applications have been added to the mobile phone. Also, the input device is expected to have a function allowing finger input through a touch panel, in addition to the conventional key-button operation. In this case, the touch panel is attached on the side of the color filter substrate of the liquid crystal display panel.
Along with the demand for a smaller overall size of the liquid crystal display device itself, there is a strong demand for a thin liquid crystal display panel, while keeping the size of the screen unchanged. In order to meet the demand for a thin liquid crystal display panel, a liquid crystal display panel is produced, and then the outside of the liquid crystal display panel is polished to a desired thickness. The liquid crystal display panel is formed by the TFT substrate including pixel electrodes, thin film transistors (TFTs), and the like, and by the color filter substrate including color filters. The two substrates constituting the liquid crystal display panel are glass substrates that are standardized, for example, to a thickness of 0.5 mm or 0.7 mm. It is difficult to obtain such standardized glass substrates from the market. In addition, a very thin glass substrate has a problem relating to mechanical strength and bending in the production process, leading to a reduction in the production yield. For this reason, the liquid crystal display panel is formed from the standardized glass substrates, and then the outside of the liquid crystal display panel is polished to a desired thickness.
The reduction of the thickness of the liquid crystal display panel poses a problem of the mechanical strength. When a mechanical stress is applied to the display surface of the liquid crystal display panel, there is a risk that the liquid crystal display panel will be destroyed. The situation is the same with the liquid crystal display panel on which the touch panel is placed, due to the small thickness of the touch panel.
In order to prevent the liquid crystal display panel from being destroyed by an external force, a front window of resin or glass is attached to the screen side of the liquid crystal display panel. In this case, an air layer is present between the liquid crystal display panel and the touch panel, or between the touch panel and the front window. The transmittance of the light from the backlight is reduced by the reflection from the interface in this area.
In order to prevent this, JP-A No. 83491/2008 describes a configuration in which an adhesive layer or an anti-reflection coating is formed between the liquid crystal display panel and the touch panel, or between the touch panel and the front window. It also describes a configuration in which a main flexible wiring substrate is attached to the liquid crystal display panel, and a touch-panel flexible wiring substrate is attached to the touch panel. The main flexible wiring substrate connects the liquid crystal display panel and the external circuit to each other. The touch-panel flexible wiring substrate connects the touch panel and the external circuit to each other. In JP-A No. 83491/2008, the touch panel is of a capacitance type and can function as a touch panel with the front window thereon.
The capacitance-type touch panel allows various operations. Such various operations can be performed by a touch-panel flexible wiring substrate including a touch-panel control IC and a touch-panel electronic component. The touch-panel flexible wiring substrate is connected to a top end of the touch panel. The size of the front window is larger than the touch panel. Thus, in order to connect the touch-panel flexible wiring substrate to the touch panel, it is necessary to increase the thickness of a bonding layer between the front window and the touch panel. Up to now, an adhesive sheet has been used as the bonding layer.
When air bubbles entering into the bonding layer or other defects are found after bonding of the touch panel and the front window, it is necessary to repair the defective part by detaching the touch panel and the front window from each other. In the repair operation, in general, the touch panel is relieved and the front window is discarded, because the touch panel is more expensive than the front window.
The touch panel and the front window are detached from each other by a cutter blade, which will be described below. However, a portion of the adhesive sheet is left on the side of the touch panel after detachment. Up to now, the residual adhesive sheet has been removed by using a cloth with a solvent. However, such a removal operation requires manpower, consequently leading to an increase in the repair cost. Further, it has often occurred that the surface of the touch panel is scratched and damaged in the removal of the adhesive material left on the touch panel.